Apparatus for use by skiers on which they may simulate the motions, exertions and techniques required in skiing has been built and sold for several years. In particular U.S. Pat. No. 3,524,641 was issued to Robert J. Ossenkop on Aug. 18, 1970, for a device comprising a movable carriage on a set of rails. The carriage of that device is constrained in its movement on the rails by flexible members attached to both the carriage and to transverse members between the rails near each end of the set of rails, and a user can move the carriage from side to side on the rails to simulate the parallel or "parallel" technique of skiing.
U.S. Pat. No. 3,547,434 was issued to the same inventor on Dec. 15, 1970. This later referenced patent is for a device similar to the first device, but comprising a number of improvements, such as moveable footrests on the carriage whereby a user may simulate turning and edging techniques in addition to parallel skiing; and, in some embodiments may also move the feet relative to one another.
The inventions referenced above each comprise a safety strap attached to a transverse member between the parallel rails and to the carriage on the rails in addition to the flexible member by which the carriage is constrained to travel on the rails. Without the safety strap a clear danger exists by virtue of the fact that the aforementioned flexible member is firmly attached to each end of the apparatus and also to the center underside of the wheeled carriage. If, during operation, the flexible member should rupture on either side, the carriage would suddenly and forcibly snap to the opposite end, and a user would almost certainly be ejected and perhaps seriously injured.
The aforementioned safety strap in the referenced inventions is fastened to a U-shaped transverse member near the center of the arched rail set and by the other end to the underside of the carriage. The length of the safety strap is such that with the carriage at its neutral position near the center of the rails the strap is loose, and has considerable slack length. The carriage may thus move a relatively long distance toward one end or the other of the rail set under only the constraint of the main flexible strap before the safety strap is straightened and will begin to extend. This distance (to either side) is approximately one half of the distance from the neutral carriage position at the center of the rail set to either end of the rail set. If the obvious accident should happen, the flexible member rupturing on one side or the other, the carriage would suddenly be propelled to the opposite side until the point at which the slack in the safety strap is "taken up", at which point the safety strap would begin to provide an increasing force in the direction opposite to the travel direction of the carriage. The safety strap is a flexible member like the main flexible member so that it can do this. This action is certainly an improvement over what would be expected if there were no safety strap, but, owing to the original slack, there would be still a period of acceleration, followed by a sudden decelleration, and certainly oscillation about the point at which the forces provided by the main flexible strap and the safety strap would balance. A user, surprised by the sudden rupture and acceleration, might still be thrown off, and perhaps injured.
One solution would be to make the safety strap shorter so that it would immediately stretch as the carriage moves to either side, but this solution has a serious drawback; the height of the carriage on the rails is short compared to the length of the rail track to either side. Being "short coupled", the safety strap would have too far to stretch, and would provide far too much force to the carriage in regular operation; and would also, by virtue of the very long stretching compared to its original length, be subject to fatigue beyong what would be prudent in design. To avoid fatigue effects, a flexible member such as the rubber straps used in this invention, should not be regularly stretched more than about 75% of its original length.
Also in regard to the arrangement of the safety strap, the U-shaped transverse member of the two referenced inventions is a single rail fastened with a single screw fastener at each end to the track rails, and the aforementioned safety strap is fastened to the bottom (central) leg of this member, near the floor. If the previously discussed accident should occur, at the point that the slack in the safety strap is all taken up, a twisting moment would be applied about an axis of rotation passing through the two screw fasteners where the transverse member is fastened to the rail set, with a magnitude equal to the force applied by the safety strap and the length of a side leg (vertical leg) of the transverse member to which the safety strap is fastened. As the carriage would continue to move under the continuing inertia of the user, this movement would increase sharply in amplitude. Under these conditions, in the apparatus shown in the two referenced inventions in the prior art, it is highly likely that there would be a sudden collapse of the transverse member in the direction of the carriage movement, adding a further sudden imbalanced movement tending to dislodge the user.
The apparatus of the prior art, while not providing adequately for the user's safety, also provides only a minimum amount of adjustability for the user to compensate for the user's weight (or mass), and to provide for changes in force against the carriage to simulate varying skiing conditions. In the referenced inventions of the prior art the only way to make such adjustments is to loosen the flexible straps at the ends of the rails away from the carriage and pre-stretch the strap, using the buckle that holds the strap around the end transverse member. Both straps have to be stretched an equal amount to accomplish such an adjustment, and there is no clear way to tell when equal adjustment has been accomplished; only the neutral position of the carriage. Furthermore, each time the bucle at one end or the other is loosened, there is an opportunity to make a mistake in the rethreading and securing of the buckle, posing an additional safety hazard for the user.
Accordingly, what is needed is a ski exercising apparatus that is safer for the user, and that has a broader range of adjustments than the exercisers of the prior art. Further, it would be desireable to have an exerciser in which the broader range of adjustments may be made conveniently and without danger of weakening the apparatus or providing other hazards, for example, leaving a main flexible member or safety strap undone or improperly assembled. Also, it would be desireable to have an apparatus that is more stable in operation and more durable than exercisers of the prior art, without adding appreciably to the cost of manufacture, and which is relatively easy to assemble, and may be packaged in a minimum volume for storage and shipment.